But his former chauffeur has another theory involving an unknown assassin, a lethal injection and the South American country's notorious military coup.

On Monday, authorities started putting that theory to the test, exhuming the poet's remains as part of a high-profile investigation that could take months to complete.

Manuel Araya, the chauffeur, said he's received threats for making the controversial claim, which has riled some of Neruda's supporters.

That won't stop him from speaking his mind, Araya told CNN Chile.

"I am not afraid of anyone," he said.

Chauffeur: 'They silenced him'

Neruda died on September 23, 1973, just 12 days after a right-wing military coup ousted socialist President Salvador Allende and brought Gen. Augusto Pinochet to power.

A view of the tomb of Chilean poet Pablo Neruda in Isla Negra, some 120 km (75 miles) west of Santiago, on April 7, 2013.

The poet, a Communist Party member, had criticized the coup and Pinochet.

Less than two weeks later, he was dead.

He had been planning to go into exile the next day -- and the timing of his death was no coincidence, according to Araya.

Neruda was a well known political and public figure, having served as a lawmaker and diplomat in addition to his literary career, which earned him a Nobel Prize in 1971.

"I believe that Pablo Neruda was murdered, because Pablo Neruda was a very relevant figure in history, as much in this country as in the world," Araya told CNN Chile. "He was going to go into exile on September 24 and they silenced him before then."

Thousands of people disappeared or died during Pinochet's rule, and many have accused his government of using death squads to wipe out political opponents.

Araya alleges that Neruda was poisoned in a clinic where he was undergoing treatment.

That claim and several other alleged discrepancies surrounding the poet's death drew the attention of Chile's Communist Party, which called for Neruda to be exhumed in 2011.

Evidence suggests that a third party was involved in Neruda's death, said Communist Party attorney Eduardo Contreras.

After the exhumation request, the head of the Pablo Neruda Foundation -- founded by the poet's widow to promote and preserve his legacy -- said he didn't want authorities to dig up Neruda's remains.

"We are against an exhumation of his cadaver because it would seem to us a true act of desecration," Juan Agustin Figueroa told Chile's Radio Bio-Bio in 2011.

The organization has since adopted a more welcoming tone.

"In this year that marks four decades since the death of Pablo Neruda, we hope also that the investigation of Judge Carroza will help clarify the doubts that might exist regarding the poet's death," the foundation said in a statement last week.

Others aren't convinced.

"This is a circus that I do not want to be part of," Bernardo Reyes, Neruda's nephew and biographer, said last week.

As debate surges, Reyes said he plans to update a biography of Neruda and publish photographs taken of the poet after his death, which show Neruda's physical state and the clothes he was wearing in his coffin.

"It seems that when someone wants to find the truth but ignores all the sides of the story, that is notable," he said.

Expert: Time 'erases evidence'

The investigation into Neruda's death follows another high-profile exhumation.

As part of a massive probe of 726 reported human rights violations during Pinochet's rule, Chilean authorities exhumed Allende's body in 2011.

Official accounts ruled the leftist leader's death a suicide, saying that he shot himself -- with a gun that was reportedly a gift from Fidel Castro -- as Pinochet's troops closed in on the presidential palace.

In July 2011, Chile's Legal Medical Service confirmed that suicide was the cause of Allende's death

For decades, Neruda has been buried alongside his wife, Matilde Urrutia, in Isla Negra, a coastal area in central Chile.

Excavation crews began work there on Sunday and completed the exhumation on Monday, CNN Chile reported.